1.2 Unregulated river
The volume reported for the opening (461 ML) and closing (481 ML) balance for unregulated river represents the sum of individual storage volumes for surface water weirs (including dead storage) operated by SA Water at 30 June 2011 and 30 June 2012 respectively. This volume includes surface water weirs that contribute to the operation of the urban water supply system through diversion to urban water storages, and for which appropriate storage height data was available to estimate total storage volume.
The surface water weir storage volume, total storage capacity and dead storage are provided in the following table.
|Surface water weir||Total storage capacity (ML)||Dead storage capacity (ML)||Storage volume at 30 June 2011 (ML)||Storage volume at 30 June 2012 (ML)|
The volume reported above does not include:
- the volume of water stored in unregulated river channels
- the volume of water stored in private on-channel storages
These volumes could not be quantified in a way that is complete, neutral and free from material error; therefore they were not reported in the water accounting statements.
Unregulated rivers include all rivers and tributaries within the major catchments in the Adelaide region and private on-channel storages, which are common throughout the region. For more information refer to the Surface water section of the 'Contextual information'. These rivers support a range of environmental, recreational and commercial activities. In particular, water from unregulated rivers is diverted for agricultural and industrial purposes as authorised by water licences and sections of the Natural Resources Management Act 2004 (South Australia). The volume of water held in unregulated rivers is an important water asset for the region. Therefore the omission of this information is significant to the users of this report.
The volume of water held within unregulated rivers is considered to be substantial and will have a material impact on the volume reported for the surface water store; however its omission is not expected to have a material impact on the surface water balance because the annual variation in the volume of water stored in river channels is assumed to be non material in comparison to annual river flow. While private on-channel storages are known to be common throughout the region, accurate information on their number and storage capacity is currently not available and it is therefore difficult to quantify their impact on the surface water store.
Storage volume was measured using gauged water level height(s) in metres with respect to the Australian height datum for individual storages. The height measurement was converted to a volume using the storage-volume relationship(s) of SA Water. The storage volume of individual surface water storages was aggregated to present the total volume for this line item.
Assumptions, limitations, caveats and approximations
- Storage-volume relationships were derived from surveys of specific parts of the individual storage (weir), and may not reflect the storage-volume relationship across the entire storage.
- Water storages are subject to sedimentation and other physical changes over time that in turn may affect the accuracy of the storage-volume relationships.